Senior Principal Scientist; Antibody Drug Conjugate

Overview

Exelixis is expanding its Antibody-Drug Conjugate (ADC) platform to advance a growing pipeline of oncology bioconjugates. We are seeking a Senior Principal Scientist with deep expertise in conjugation chemistry to serve as the technical anchor for ADC generation, from discovery‑scale screening through early process development and IND‑enabling toxin supply.

• Design, execute, and optimize ADC conjugation reactions at mg‑to‑multigram scale to support discovery screening, in‑vivo pharmacology, and early CMC deliverables.
• Apply and advance both stochastic (interchain cysteine) and site‑specific conjugation platforms (engineered cysteine, transglutaminase, sortase, glycan remodeling, unnatural amino acids, native disulfide re‑bridging) and contribute to the evaluation and adoption of new platforms.
• Optimize stoichiometry, linker chemistry, conjugation reaction conditions, and buffer systems to control drug‑to‑antibody ratio (DAR), homogeneity, and aggregation.
• Purify conjugates via FPLC, TFF/UF‑DF, and preparative chromatography; develop and validate formulation buffers for bioconjugate stability.
• Characterize ADCs by HIC, SEC, RP‑HPLC, LC‑MS (intact&reduced), and UV‑Vis; interpret data to inform process and molecular design decisions.
• Partner with analytical development to establish critical quality attributes (CQAs) and in‑process controls for lead candidates.
• Serve as the Biotherapeutics group’s conjugation subject‑matter expert, provide go/no‑go technical read on lead molecule DAR strategy, linker selection, and develop ability.
• Help design and interpret in‑vitro bio‑functional assays (efficacy, bystander, catabolite/metabolite , MoA studies) in collaboration with biology and DMPK teams.
• Author technical reports, patents, and manuscripts; present findings at program reviews and external scientific venues.
• Track and integrate emerging conjugation technologies, linker‑payload chemistries, and IP developments to shape platform investment.
• Partner with Protein Science, ADC Chemistry, Analytical, DMPK, Toxicology, and CMC/Process Development to deliver quality material on aggressive timelines.
• Manage select CRO/CDMO relationships for outsourced conjugation, analytics, or scale‑up activities; support technology transfer.
• Follow all IP, EH&S, and laboratory compliance policies.

• BS/BA in Chemistry, Biochemistry, Chemical Biology, or related discipline and a minimum of 13years of related experience; or MS/MA with 11years; or PhD with 8years; or an equivalent combination of education and experience.
• Hands‑on mastery of ADC conjugation chemistry from discovery through early CMC with a track record of advancing molecules to development‑candidate nomination.
• Demonstrated experience in DAR control, product homogeneity optimization, and formulation of bioconjugates.
• Preferred experience with site‑specific conjugation platforms (e.g., engineered cysteine, THIOMAB, transglutaminase/AIICAP, glycan remodeling, sortase, click chemistry).
• Experience with dual‑payload conjugates, bispecific ADCs, or antibody‑oligonucleotide conjugates.
• Working knowledge of linkers (cleavable and non‑cleavable), payload classes, and their mechanisms of action.
• Fluency with HIC, SEC, RP‑HPLC, and LC‑MS for conjugate characterization.
• Rigorous scientific problem‑solving and excellent written and oral communication; proven collaborator across chemistry, biology, and CMC.
• Preferred familiarity with early process development, technology transfer, and CDMO management under GLP/GMP supply.
• Patents and peer‑reviewed publications in bioconjugation.
• Working knowledge of the ADC IP landscape.

Base salary range: $169,500–$239,500 annually (commensurate with geographic location). In addition to base salary, Exelixis offers a comprehensive benefits package, including a 401(k) plan with generous company contributions, group medical, dental, and vision coverage, life and disability insurance, and flexible spending accounts. Employees may also participate in a discretionary annual bonus program and, for field‑sales staff, a sales‑based incentive plan. Opportunities to purchase company stock and receive long‑term incentives are available.

Vacation: 15 accrued days in the first year; 17 paid holidays (including a company‑wide winter shutdown), up to 10 sick days annually.

We are an Equal Opportunity Employer and do not discriminate against any employee or applicant for employment because of race, color, sex, age, national origin, religion, sexual orientation, gender identity, status as a veteran, and basis of disability or any other federal, state or local protected class.